1. Field of the Invention
This invention relates generally to an automatic transmission for motor vehicle, and, more particularly, to integrating an auxiliary oil pump, electric drive system and the hydraulic control and supply circuit of the transmission.
2. Description of the Prior Art
An electrical starting motor is used to crank and start an engine in an automotive vehicle equipped with an automatic transmission. To improve vehicle fuel economy, a stop-start engine cranking system automatically turns the engine off when the accelerator pedal is released, the brake pedal is depressed and the vehicle speed is substantially zero for a predetermined period, provided the state of charge of a battery that powers the starting motor is sufficiently high. The engine cranking system automatically restarts the engine in response to the vehicle operator's releasing the brake pedal and depressing the accelerator pedal, indicating a desire to accelerate the vehicle. These actions occur without need to turn the ignition key either on or off.
To avoid producing an engine speed flare upon restarting the engine, the transmission control elements, i.e., the friction clutches and brakes that produce drive in the startup gear, are stroked to take up clearances in the servos that actuate the control elements, and a low magnitude of torque transmitting capacity is produced in those friction elements, thereby reinstating the vehicle creep function whereby the vehicle moves in gear at low speed.
Automatic transmission fluid at line pressure is supplied to the friction elements for this purpose. An auxiliary oil pump driven by an electric motor and powered by an electric storage battery is provided to maintain pressure in the friction elements
The auxiliary pump must be able to draw oil from the transmission's oil sump and supply flow to the hydraulic control's valve body. Adding the electric motor and oil pump to an automatic transmission to support the stop/start function usually requires significant changes to the transmission. Usually the valve body, transmission case, converter housing and sometimes, even the base mechanical pump are modified to achieve the engine start/stop function.
A need exists in the industry for a technique or system that readily and reliably connects an auxiliary oil pump to a transmission oil sump and to a passage that carries pressurized fluid to friction elements of the transmission.